A lithium battery using a lithium metal as a negative electrode has excellent energy density. However, with repeated cycles, such a battery can be subject to dendrites' growths on the surface of the lithium metal electrode when recharging the battery as the lithium ions are unevenly re-plated on surface of the lithium metal electrode. To minimize the effect of the morphological evolution of the surface of the lithium metal anode including dendrites growth, a lithium metal battery typically uses a mechanical system that applies pressure onto the multiple laminates of the electrochemical cells, each laminate of the electrochemical cells including a solid polymer electrolyte having sufficient mechanical strength to withstand the applied pressure as described in U.S. Pat. No. 6,007,935 which is herein incorporated by reference. The mechanical strength and shear modulus of the solid polymer electrolyte combined with mechanical pressure applied onto the lithium metal electrode is believed to inhibit the growth of dendrite on the surface of the lithium metal electrode or at least substantially reduce the dendrite growth velocity over hundreds of charge-discharge cycle such that a lithium battery using a lithium metal anode may have a long service life. However, dendrites may eventually form on the surface of the lithium metal anode and may still grow to penetrate the electrolyte, even though the electrolyte is solid and proven to be an effective barrier against perforation of dendrites. Dendrites' growth may ultimately cause ‘soft’ short circuits between the negative electrode and the positive electrode, resulting in decreasing or poor performance of the battery. The growth of dendrites may still limit the cycling characteristics of a solid polymer electrolyte battery and therefore still constitutes an important obstacle with respect to the optimization of the performances of lithium batteries having a metallic lithium anode.
The Li dendrite growth during the Li deposition process or re-plating on the surface of the Li metal anode which occurs when the electrochemical cell is recharged has been extensively studied over the years in order to reveal the mechanisms of dendrite formation and the growth processes in an effort to find approaches to suppress or prevent the dendrite formation. It was found that different dendrite morphologies are formed at different current densities during recharge. At low current density, needle-like and particle-like dendrites are observed whereas at higher current densities tree-like or bush-like dendrites are observed. The evolution of tree-like and needle-like dendrites being more problematic as the branches of the tree-like dendrites or the needles of the needle-like dendrites are more likely to perforate the solid polymer electrolyte as they grow to eventually contact the opposite positive electrode thereby causing a short circuit.
Other investigations revealed swelling and shrinking of the surface of the Li film during repeated Li deposition (charge) and Li stripping (discharge) causing cracks along the grain boundaries of the structure the Li film which become preferential locations on the surface for Li deposition and therefore dendrite formation and growth. Another study demonstrated that the bulk of the dendrite structure lay within the Li electrode, underneath the polymer electrolyte/Li electrode interface at the early stage of dendrite development and that crystalline impurities in the Li electrode were found at the base of the subsurface dendritic structure pointing to the importance of the purity of the lithium metal electrode.
It was also found that temperature and electrolyte composition strongly impact the Li deposition morphology leading to dendrite formation and growth.
Furthermore, it has been shown that when the electrolyte is polarized under high current density, Li+ cations near the surface of the electrode are reduced to Li metal such that the Li+ cation concentration decreases resulting in anion migrating toward the positive electrode until a new equilibrium is reached thereby depleting the surface of the Li metal electrode of anions in specific locations on the surface of the Li metal where the anionic concentration falls to zero resulting in instability at the interface of the Li electrode and electrolyte from erratic and inconsistent distribution of the surface potential, which creates localized electric field that leads to dendrite formation and growth due to preferential path for Li deposition.
Several models were conceived to explain the mechanisms of dendrite formation and the growth processes on the surface of a Li metal electrode; however no real solution has been provided to date to suppress or prevent the dendrite formation. Thus, there is a need for an electrochemical cell configuration including a Li metal electrode which is specifically adapted to suppress, prevent or strongly inhibit dendrite formation and growth on the surface of the Li metal electrode through repeated cycles of charge and discharge.